As radio frequency (RF), microwave, and millimeter-wave communication systems and devices continue to proliferate, there is an increasing need for more compact and efficient amplifiers in these frequency bands that can produce a desired output signal level.
FIG. 1 shows an amplifier 100 having an input port 102 configured to receive an input signal (e.g., an RF, microwave, or millimeter wave signal) and an output port 104 configured to output an amplified output signal. The input signal and the amplified output signal may be signals at an operating frequency of amplifier 100 at which amplifier 100 provides an amplification or gain. Amplifier 100 includes gain element 110, input matching network 140, and output matching network 150. Various conventional elements providing DC bias voltages and DC bias currents to gain element 110 and not forming a part of the RF/microwave/millimeter-wave signal path are omitted from FIG. 1 for simplification of the drawing and the description to follow.
Gain element 110 includes an input terminal (e.g., a gate) 112, and output terminal 114 (e.g., a drain or source), and a third terminal 116 (e.g., a source or drain) which is connected to a power supply voltage (e.g., ground). In a beneficial arrangement gain device 110 comprises a field effect transistor (FET). However, other gain elements such as bipolar transistors could be employed instead.
Input matching network 140 is an impedance matching arrangement that attempts to match the output impedance (e.g., 50 ohms; 75 ohms) of an element supplying the input signal to amplifier 100 via input port 102, to the input impedance at the input terminal (e.g., gates) 112 of gain device 110 at an operating frequency or frequencies of amplifier 100. Similarly, output matching network 150 is an impedance matching arrangement that attempts to match the output impedances at the output terminal (e.g., drain) 114 of gain device 110 to an input impedance (e.g., 50 ohms; 75 ohms) of an element (e.g., an antenna) receiving the amplified output signal from amplifier 100 via output port 104.
Input matching network 140 comprises: inductor 142 connected between an input terminal 102 of amplifier 100 and an input terminal 112 of gain device 110, and a capacitor 144 connected between input terminal 112 of gain device 110 and ground. Output matching network 150 comprises: inductor 152 connected between an output terminal 114 of gain device 110 and an output terminal 104 of amplifier 100, and a capacitor 154 connected between output terminal 114 of gain device 110 and ground.
Usually, input and output impedance matching networks 140 and 150 are designed based on filter synthesis theory. Amplifier 100 illustrates a low-pass-filter based design for input and output ports.
To achieve a larger output power, a power amplifier may employ a larger gain device, for example a larger FET that has a larger gate periphery. Depending upon the configuration, at very high operating frequencies (e.g., at millimeter wave frequencies) an input coupling structure (which may also be referred to as input connecting structure) for the input (e.g., gate) of this lamer gain device, and/or an output coupling structure (which may also be referred to as an output connecting structure) for the output (e.g., drain) of this larger gain device may cause the gain device to effectively constitute a plurality of smaller individual gain elements that are effectively, or almost, connected in parallel with each other. These individual gain elements are only effectively, or almost, in parallel with each other and arc not truly in parallel with each other because of the inductances and/or capacitances of the input and output coupling structures mentioned above, which in effect form part of the input and output matching networks for the amplifier. Thus, from a macroscopic viewpoint, the amplifier may be considered to include a single, larger, gain device, while from a microscopic viewpoint, the amplifier may be considered to include a plurality of individual gain elements, which, for example, may share portions of their source and/or drain regions and/or ground contacts, but whose input and/or output terminals are actually and electrically separated by inductances and/or capacitances of the input and/or output coupling structures.
However, when the configurations of the input connecting structure and/or output connecting structure are asymmetrical with respect to the individual gain elements (e.g., FETs), this can create phase imbalances between the inputs and/or outputs of the individual gain elements (e.g., FETs). These phase imbalances for feeding the input signal to the individual gain elements (e.g., FETs) and for extracting the output signal from the individual gain elements (e.g., FETs) can create serious power degradation for the amplifier at very high frequencies such that the amplifier produces a reduced output power.
What is needed, therefore, are input and output matching networks for an amplifier, including coupling structures, which can reduce or eliminate phase imbalances between individual gain elements of the amplifier. What is also needed is an amplifier including such input and output matching networks.